Active noise control apparatus (hereinafter referred to as “ANC apparatus”) are known as apparatus for controlling acoustics in relation to a vibration noise in vehicular passenger compartments. General ANC apparatus reduce a vibration noise by outputting a canceling sound that is in opposite phase with the vibration noise from a speaker in the vehicular passenger compartment. An error between the vibration noise and the canceling sound is detected as remaining noise by a microphone that is disposed in the vicinity of an ear of the driver of the vehicle, and is used to determine a subsequent canceling sound. Some ANC apparatus reduce a noise (muffled engine sound) that is generated in the passenger compartment as the engine operates (vibrates), and other ANC apparatus reduce a noise (road noise) that is generated in the passenger compartment as the road wheels are in rolling contact with the road while the vehicle is traveling {see, for example, U.S. Patent Application Publication No. 2004/0247137 (hereinafter referred to as “US 2004/0247137 A1”), Japanese Laid-Open Patent Publication No. 06-083369 (hereinafter referred to as “JP 06-083369 A”), and Japanese Laid-Open Patent Publication No. 2007-216787 (hereinafter referred to as “JP 2007-216787 A)}.
According to JP 06-083369 A, vibrations of the front road wheels are detected by a pickup (1) near the front road wheels. A canceling sound for canceling a vibration noise due to the vibrations of the front road wheels is generated based on an output signal (reference signal) from the pickup (1). The output signal (reference signal) from the pickup (1) is delayed by a delay circuit (4) depending on the vehicle speed. A canceling sound for canceling a vibration noise due to the vibrations of the rear road wheels is generated based on the delayed reference signal (see, for example, Abstract, FIG. 1, and paragraphs [0018] through [0026]).
According to JP 2007-216787 A, vibrations applied from the front road wheels to the vehicle body are detected by acceleration sensors (14, 16) near the front road wheels. Based on accelerations detected by the acceleration sensors and a vehicle speed detected by a vehicle speed sensor (26), a rear vibration estimator (20) estimates vibrations applied from the rear road wheels to the vehicle body. A canceling sound is output based on the vibrations estimated as being applied from the rear road wheels and a sound detected by a microphone (30) (see Abstract and FIG. 1).